Oxydiphthalic anhydride is commonly used as a monomer component to form a unique class of high temperature polyetherimides. Oxydiphthalic anhydrides can generally be prepared by coupling two halophthalic anhydrides in the presence of an inorganic carbonate, a solvent, and a catalyst. The crude product of such a reaction often includes the solvent, unreacted starting materials, catalyst, and other impurities, which must be separated from the oxydiphthalic anhydride prior to its use in polymer synthesis. Residual impurities have been shown to have an adverse effect on the thermal stability of the resulting polymers.
The purification of anhydrides has thus been the focus of extensive research and development. Despite the previous research efforts, there remains a need for an improved purification process for oxydiphthalic anhydrides. It would be particularly advantageous to provide a more efficient method for the purification of oxydiphthalic anhydrides that could remove substantially all residual reactants, reaction intermediates, and residual catalyst.